1. Technical Field
The present invention relates to a resonance-type non-contact power supply system, and a power-receiving-side device and a power-transmission-side device which are used in the resonance-type non-contact power supply system.
2. Background Art
A technique in which electric power is supplied to a load device by a non-contact system is known. In recent years, the non-contact power supply system is practically used even as a power supply system for electric vehicles, various standards are established, and safety for common use is considered.
There are various types of non-contact power supply system. A power supply system for electric vehicles is a resonance-type non-contact power supply system, which is shown in FIG. 1A, which greatly attracts attentions and whose basic principle is developed and demonstrated by Massachusetts Institute of Technology (MIT) (for example, refer to JP-A-2009-501510). The resonance-type non-contact power supply system shown in the figure includes a resonance system of a high frequency power supply, resonance coils (primary and secondary resonance coils) and a load that transmits electric power non-contactly. Specifically, power-transmission-side (primary side) devices include a high frequency power supply, a primary coil, and a primary resonance coil. Power-receiving-side (secondary side) devices include a secondary resonance coil, a secondary coil and a load. The power-transmission-side devices and the power-receiving-side devices in the system have an advantage of being able to supply electric power to a place spaced several meters with a high transmission efficiency (sometimes around 50%) by being magnetically coupled (electromagnetically coupled) by resonance.
In the technique of MIT shown in FIG. 1A, the resonance system is assumed to be configured with “a power supply part (the high frequency power supply and the primary coil), a resonance part (the primary resonance coil and the secondary resonance coil), and a load part (the secondary coil and the load)”. However, additional components become necessary when the non-contact power supply system is mounted in an electronic device or an automobile power supply system. A system configuration example where the system of FIG. 1A is mounted in a real system is shown in FIG. 1B. As shown in the figure, in the real system, a transmission path between the power supply and a primary resonance coil part and a transmission path between a secondary resonance coil part and the load are necessary.
Related art is also disclosed in JP-A-2010-40699 and JP-A-5-344602.
A resonance-type non-contact power supply system 510 that is more specifically configured than in FIG. 1B is shown in FIG. 2. As shown in the figure, when coaxial cables (a power-transmission-side coaxial cable 60 and a power-receiving-side coaxial cable 70) are used, there are the following problems.    (1) When a coaxial cable is used for the transmission path, an electric current flows through not only the inner side but also the outer side of a coaxial cable outer conductor 64 of the primary coaxial cable (the power-transmission-side coaxial cable 60), and a radiated electromagnetic field occurs.    (2) Because part of the electromagnetic field from a primary coil 30 is coupled with the coaxial cable outer conductor 64 and an induced current flows, a radiated electromagnetic field occurs.    (3) Because all of the electromagnetic field from a secondary resonance coil 45 is not necessarily coupled with a secondary coil 40, part of the electromagnetic field is coupled with a coaxial cable outer conductor 74 of a power-receiving-side coaxial cable 70, and an induced current flows, a radiated electromagnetic field occurs.
An example in which the resonance-type non-contact power supply system 510 is applied to a charging system for electric vehicles or the like is shown in FIGS. 3A and 3B. Power-transmission-side (primary side) devices (20, 30 and 35) are arranged underground. When a vehicle 1 including power-receiving-side (secondary side) devices (50, 40 and 45) is placed above the power-transmission-side devices, non-contact power transmission is enabled. Since it is necessary for the charging system for electric vehicles to transmit electric power in a short time, it is thought that large electric power transmission that exceeds, for example, 1 kW is demanded. However, as shown in FIG. 3A, when the large electric power transmission is performed, a radiated electromagnetic field more than a reference value (DA) of ICNIRP human body protection guidelines may occur between the primary resonance coil 35 and the secondary resonance coil 45, that is, between the vehicle and the road surface. When the radiated electromagnetic field leaks out in a wide area, a human body M1 and electronic devices may be adversely affected. Therefore, as shown in FIG. 3B, in order that a danger zone where the electromagnetic field strength exceeds a reference value of ICNIRP human body protection guidelines may not be entered, measures to surround an area (the danger zone) where the transmission is performed with a shielding such as a fence 2 are considered. However, if a child M2 or a small animal P2 such as a pet who cannot understand a rule enters the danger zone, an accident may happen. Furthermore, it is considered to construct a system which stops charging immediately when sensors which are arranged in several places and sense whether the danger zone is entered recognize an entry. However, it is difficult to decide criteria for an object that entered the danger zone when the number of the sensors increases.